Method and device for transmitting and receiving broadcast signal

ABSTRACT

The present invention relates to a device and a method for transmitting and receiving a broadcast signal comprising a subtitling service. Provided in one embodiment of the present invention is a method for transmitting a broadcast signal, the method comprising the steps of: generating a broadcast signal comprising video data and subtitle data; and transmitting the generated broadcast signal. According to the embodiment of the present invention, a transport stream providing a digital broadcast subtitling service using an XML subtitle may be transmitted.

This application is a National Stage Application of InternationalApplication No. PCT/KR2015/007203 filed on Jul. 10, 2015, which claimsthe benefit of U.S. Provisional Application No. 62/023,198, filed Jul.11, 2014, all of which are hereby incorporated by reference in theirentirety for all purposes as if fully set forth herein.

TECHNICAL FIELD

The present invention relates to a method and device for transmittingand receiving a broadcast signal.

BACKGROUND ART

With development of digital technology and communication technology,dissemination of and demand for multimedia content centered onaudio/video in various fields including the Internet and personal mediaas well as broadcast and movie have rapidly increased. Further, consumerdemand for realistic media for providing three-dimensional effectsthrough broadcast and movie has increased. In addition, with developmentof display technology, TV screens used in households have been enlargedand thus consumption of high-quality content such as high definition(HD) content has increased. Along with 3DTVs, a realistic broadcast suchas ultra high definition TV (UHDTV) has attracted attention as anext-generation broadcast service. In particular, a discussion about anultra high definition (UHD) broadcast service has been increased.

A current broadcast subtitle service is being provided in the form ofclosed captioning or digital video broadcasting (DVB) subtitles. SinceDVB subtitles are provided in the form of a. bitmap image, subtitleshaving different sizes should be provided to images having various sizesor subtitles having a single size should be scaled. At this time,bandwidth efficiency may deteriorate in the former case and scalingsharpness may deteriorate in the latter case. In particular, recently,since HD broadcast services using UHDTVs have been actively discussed,necessity of a new broadcast subtitle service has emerged.

DISCLOSURE Technical Problem

An object of the present invention is to increase transmissionefficiency in a method and device for transmitting a broadcast signal.

Another object of the present invention is to provide a transmissionmethod and device for providing a subtitle service in a broadcastnetwork.

Another object of the present invention is to provide a broadcast methodand device capable of improving quality of a subtitle service.

Technical Solution

A method of transmitting a broadcast signal according to an embodimentof the present invention may include generating the broadcast signalincluding video data and subtitle data and transmitting the generatedbroadcast signal.

In the method of transmitting the broadcast signal according to theembodiment of the present invention, the subtitle data may include XMLsubtitle data.

In the method of transmitting the broadcast signal according to theembodiment of the present invention, the XML subtitle data may includesubtitle text and subtitle metadata.

In the method of transmitting the broadcast signal according to theembodiment of the present invention, the subtitle metadata may includeinformation corresponding to a wide color gamut and a high dynamic rangefor a high-quality broadcast.

In the method of transmitting the broadcast signal according to theembodiment of the present invention, the subtitle metadata may includeinformation on a color gamut of subtitles, a dynamic range of thesubtitles and a bit depth of the subtitles.

A method of receiving a broadcast signal according to an embodiment ofthe present invention may include receiving the broadcast signalincluding video data and subtitle data and processing and outputting thevideo data and the subtitle data.

In the method of receiving the broadcast signal according to theembodiment of the present invention, the subtitle data may include XMLsubtitle data.

In the method of receiving the broadcast signal according to theembodiment of the present invention, the XML subtitle data may includesubtitle text and subtitle metadata.

In the method of receiving the broadcast signal according to theembodiment of the present invention, the subtitle metadata may includeinformation corresponding to a wide color gamut and a high dynamic rangefor a high-quality broadcast.

In the method of receiving the broadcast signal according to theembodiment of the present invention, the subtitle metadata may includeinformation corresponding to a wide color gamut and a high dynamic rangefor a high-quality broadcast.

In the method of receiving the broadcast signal according to theembodiment of the present invention, the subtitle metadata may includeinformation on a color gamut of subtitles, a dynamic range of thesubtitles and a bit depth of the subtitles.

In the method of receiving the broadcast signal according to theembodiment of the present invention, the video data further includesvideo metadata.

The method of receiving the broadcast signal according to the embodimentof the present invention may further include detecting whether thesubtitle metadata and the video metadata match.

The method of receiving the broadcast signal according to the embodimentof the present invention may further include converting the subtitlemetadata if the subtitle metadata and the video metadata do not match.

Advantageous Effects

According to the embodiments of the present invention, it is possible toincrease transmission efficiency in a method and device for transmittinga broadcast signal.

According to the embodiments of the present invention, it is possible toprovide a high-quality subtitle service in a broadcast network.

According to the embodiments of the present invention, a broadcastreception device may extract and display a subtitle included in abroadcast signal.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing an XML based broadcast subtitle serviceaccording to an embodiment of the present invention.

FIG. 2 is a diagram showing operation of a receiver related to XML basedsubtitles according to an embodiment of the present invention.

FIG. 3 is a diagram showing a preprocessing procedure of subtitles in abroadcast receiver according to an embodiment of the present invention.

FIG. 4 is a diagram showing mapping of dynamic range to luminanceaccording to an embodiment of the present invention.

FIG. 5 is a diagram showing a method of transmitting metadata ofsubtitles according to an embodiment of the present invention.

FIG. 6 is a diagram showing a detailed description of elements ofmetadata of subtitles according to an embodiment of the presentinvention.

FIG. 7 is a diagram showing a detailed description of elements ofmetadata of subtitles according to an embodiment of the presentinvention.

FIG. 8 is a diagram showing an additional description of elements ofmetadata. of subtitles according to an embodiment of the presentinvention.

FIG. 9 is a block diagram showing a broadcast transmitter according toan embodiment of the present invention.

FIG. 10 is a block diagram showing a broadcast receiver according to anembodiment of the present invention.

FIG. 11 is a diagram showing the configuration of a broadcast receiveraccording to an embodiment of the present invention in detail.

FIG. 12 is a diagram showing a method of transmitting a broadcast signalincluding XML subtitles according to an embodiment of the presentinvention.

FIG. 13 is a diagram showing a method of receiving a broadcast signalincluding XML subtitles according to an embodiment of the presentinvention.

BEST MODE

As a broadcast service starts to be provided through Internet protocol(IP) as a next-generation broadcast service, a new subtitle servicestandard which will replace existing broadcast subtitles wasestablished. A combination of an existing broadcast and an IP will beprovided as a future broadcast service. At this time, when subtitlesgenerated according to different standards are provided, efficiency maydeteriorate.

The present invention describes a method of providing a subtitle servicein old and new receivers based on high-quality image elements such asWCG, HDR and higher bit depth upon providing a digital image subtitleservice using XML subtitles (TTML, SMPTE-TT, EBU-TT-D, etc.).

Recently, a standard of subtitles based on XML such as time text markuplanguage (TTML) and EBU time text (EBU-TT) has been established.Although this standard aims at a subtitle service in a media and IPstreaming environment, standard groups such as DVB and ATSC attempt touse this standard even in a broadcast service. To this end, it ispossible to use a unified subtitle source in various broadcastenvironments and to adaptively use the same subtitle source in variousservice environments (e.g., HD, UHD, etc.).

XML based subtitles are being considered as a UHD based next-generationsubtitle service method, since XML based subtitles are configured tosupport video having various sizes and are suitable for an IP streamingbased service. Change from HD to UHD leads to resolution improvement andchange in various image quality aspects such as dynamic range, colorgamut, and bit depth. Therefore, in a next-generation subtitle service,such image elements need to be considered. However, current TTML basedXML subtitles do not consider such elements and needs to considerelements such as WCG and HDR in order to cope with various serviceenvironments.

Hereinafter, a method of providing a suitable subtitle service even whena subtitle production environment and a display environment aredifferent in terms of the image quality elements such as color gamut andluminance range in provision of an XML based broadcast media subtitleservice will be described.

In the present invention, as a method of utilizing subtitles producedbased on XML in a broadcast media service, XML subtitles metadataservice method capable of delivering information on a productionenvironment of XML subtitles in order to support receivers and displayshaving various capabilities in terms of HDR and WCG will be described.

In addition, the present invention proposes a method of expressing amaximum of 16 bits while continuously supporting an existing 8-bitsystem in a state in which the bitdepth of XML subtitles is restrictedto 8 bits.

In addition, in the present invention, operation of a receiver relatedto color gamut, dynamic range and bit depth when a subtitle productionenvironment and an image reproduction environment are different will bedescribed.

For understanding of the present invention and convenience ofdescription, terms and abbreviations will be defined as follows.

HEVC (High Efficiency Video Coding) is a high-efficiency video codingstandard for providing the same video quality with a compression ratiowhich is about twice that of existing H.265/AVC technology.

XML (Extensible Markup Language) is a language produced by improving anHTML and can improve a homepage establishment function, a searchfunction, etc. and easily process complex data of a client system, Inthe present invention. XML is used as a language configuring subtitledata and XML subtitles may include a head and a body.

A PTS (Presentation Time Stamp) may mean a value indicating a time whena decoded access unit is reproduced. In the present invention, the PTSmay be used to synchronize a video ES with a subtitle ES.

An ES (Elementary Stream) may mean output of a data encoder. That is,outputs of a video encoder and an audio encoder may be defined as avideo ES and an audio ES, respectively. In the present invention, XMLsubtitles ES may be defined and used.

A TS (Transport Stream) refers to a transport stream including one orseveral programs in an MPEG-2 system and may be used in a transportmedium with transmission errors. In the present invention, the TS maymean a transport stream in which at least two of a video ES, an audio ESand a subtitle ES are multiplexed and transmitted.

FIG. 1 is a diagram showing an XML based broadcast subtitle serviceaccording to an embodiment of the present invention. FIG. 1 is a diagramshowing an end-to-end system including a transmitter and a receiver fora digital broadcast service. The XML based subtitles used in the presentinvention is not influenced by the size of video and thus is applicableto UHD/HD/SD.

A transmitter may transmit compressed video and XML subtitles modifiedfor transmission through a multiplexer. In addition, a receiver maydemultiplex a received signal and then provide subtitles through imagedecoding and an XML parser. A graphics engine may modify a subtitleexpression method according to the environment of the receiver andoutput the subtitles to a display processor. The display processor mayoutput the decoded video and the subtitles.

In FIG. 1, the transmitter may receive video data and subtitleinformation. The resolution of video data input to the transmitter maybe UHD, HD or SD. In addition, the subtitle information input to thetransmitter may be described in XML. The video data input to thetransmitter may he encoded by an encoder in the transmitter (101). Thetransmitter may use high efficiency video coding (HEVC) as a method ofencoding video data. The transmitter may synchronize and multiplex theencoded video data and the XML subtitles using a multiplexer (102).Here, the XML subtitles may be modified for transmission. A method ofmodifying XML subtitles and a method of generating metadata of the XMLsubtitles will be described in detail below. The transmitter may performchannel coding and modulation with respect to the multiplexedsynchronized data and transmit the data as a broadcast signal.

The receiver may receive the broadcast signal and perform demodulationand transport packet decoding. In addition, the receiver may demultiplexthe decoded transport packet and perform video decoding and XML parsing.XML parsing may be performed through an XML parser. Here, the videodecoder and the XML parser may exchange metadata. Such metadata may beused as supplementary information upon displaying the video and thesubtitles. The receiver may demodulate the received broadcast signal andperform transport packet decoding (104). The decoded transport packet isinput to a video decoder 106 and an XML parser 107 after passing througha demultiplexer 105. Here, the video decoder 106 may decode UHD, HD orSD video data according to the resolution of the received video data. Inaddition, the XML parser 107 may extract the XML subtitles. In thisprocess, the receiver may consider image elements in display of thevideo data and the XML subtitles using the metadata. Here, the imageelement may include dynamic range, color gamut, bit depth, etc., forexample. In particular, in the present invention, if a wide color gamut(WCG) and a high dynamic range (HDR) of UHD image quality elements areincluded in a service (e.g., DVB UHD-1 phase 2, RD UHD-FE, etc.),information on the image quality elements which are used as a subtitleproduction criterion may be provided to the receiver. To this end, if asubtitle production environment and a display environment are different,the receiver may appropriately modify the color or luminance of thesubtitles according to the display environment. The graphics engine 108may modify the expression method of the XML subtitles in correspondencewith the above-described image elements. The decoded video data and theXML subtitles, the expression method of which is modified, may beprocessed and displayed by the display processor 109.

FIG. 2 is a diagram showing operation of a receiver related to XML basedsubtitles according to an embodiment of the present invention. Thereceiver may analyze content of the XML based subtitles through an XMLparser. In addition, the receiver may deliver the content of thesubtitles, information for expressing the subtitles and spatialinformation of the subtitles to a graphics engine. Here, the informationfor expressing the subtitles may include at least one of font, colorand/or size information. In addition, the spatial information of thesubtitles may include at least one of region and/or resolutioninformation. The receiver of the present invention may perform apreprocessing procedure prior to delivery of the subtitles andinformation on the subtitles to the graphics engine. That is, apreprocessing procedure of detecting whether the subtitle productionenvironment and the display environment of the receiver are differentand transforming the subtitles may be performed. The receiver maydeliver the subtitle information transformed through preprocessing tothe graphics engine. The graphics engine may generate subtitles usingthe content of the subtitles or the information on the transformedsubtitles and deliver the subtitles to a display processor.

FIG. 3 is a diagram showing a preprocessing procedure of subtitles in abroadcast receiver according to an embodiment of the present invention.The preprocessing procedure may include a step of detecting whether asubtitle production environment and a display environment match and aconversion step. The receiver may detect or determine whether thesubtitle production environment and the display environment match basedon metadata of a target video format of subtitles and metadata of adisplay of the receiver. The metadata of the target video format of thesubtitles may include bitdepth, dynamic range and color gamutinformation. At this time, a determination criteria may be deliveredthrough metadata in XML, and EBU-TT-D may be delivered to the receiverthrough ebuttm:RefGamut, ebuttm:RefDynamicRange, ebuttm:EOTF,ebuttm:RefBitDepth. Although the information is defined in the EBU-TT-Dmetadata in the above description, the same information may be definedin TTML metadata (ttm), parameter (ttp) and style (tts). That is, theelements newly defined in the present invention are applicable to XMLbased subtitle standards such as TTML, EBU-TT, SMPTE-TT, CFF-TT, Youviewand EBU-TT. In the present invention, gamut, dynamic range and bitdepthare used as comparison criteria and resolution and aspect ratio may beused as comparison criteria if necessary. In addition, the metadata ofthe display of the receiver may include display environment informationand may include the bitdepth, dynamic range and color gamut informationof the display of the receiver.

In the matching step, if the metadata of the subtitle productionenvironment and the metadata of the display environment match, subtitletext data and subtitle metadata are delivered to the graphics engine forhigh-end display. That is, if it is determined that the target videoformat of the subtitles matches the metadata of the display or isacceptable, the procedure progresses to a next step without processing.Here, determining that the target video format of the subtitles matchesthe metadata of the display or is acceptable may mean that video isHDR/WCG video or the display is an HDR/WCG display. The graphics enginemay generate subtitles using the received subtitle text data and themetadata of the subtitles and deliver the generated subtitles to thedisplay processor.

In contrast, if it is determined that the metadata of the subtitles doesnot match the display environment, that is, if the expression method ofthe subtitles needs to be converted, the preprocessing procedure mayinclude a step of converting a subtitle expression method in terms ofthe color and luminance of the subtitles. In the conversion step, thesubtitle expression method included in the metadata of the subtitles maybe converted based on the metadata of the target video format of thesubtitles and the metadata of the display of the receiver. That is, thebitdepth, dynamic range or color gamut included in the metadata of thesubtitles may be converted and the modified bitdepth, modified dynamicrange and modified color gamut may be delivered to the graphics engine.The transformed metadata and subtitle text may be delivered to agraphics engine for mid-end or low-end display. The graphics engine maygenerate subtitles based on the received subtitle text data and thetransformed metadata of the subtitles and deliver the generatedsubtitles to the display processor. In the preprocessing procedure, eachelement is converted if the metadata of the subtitles and the metadataof the display differ in terms of color gamut, dynamic range orbitdepth. The conversion step is based on color gamut, dynamic range,EOTF and bitdepth information, which is reference information deliveredthrough ebuttm:RefGamut, ebuttm:RefDynamicRange, ebuttm:EOTF andebuttm:RefBitDepth newly defined in the metadata and (1) the differencemay be ignored or (2) color gamut mapping or dynamic range mapping maybe performed.

The graphics engine performs transformation for reproducing textinformation as video information and the receiver performs displayprocessing with respect to the output of the graphics engine andcombines the video, the subtitles and the other elements configuring thevideo to configure final display video.

FIG. 4 is a diagram showing mapping of a dynamic range to luminanceaccording to an embodiment of the present invention. That is, mapping ofa dynamic range to luminance of XML based subtitles is shown. Morespecifically, an example of a method of reproducing XML subtitlesproduced for HDR video in an SDR display environment is shown. If aluminance range used in the HDR video is broader than that supported bythe display of the receiver, the luminance of video is changed throughdynamic range mapping. At this time, if only the luminance of video ischanged without considering the luminance range of the subtitles, thesubtitles may not be suitable for change in luminance of the surroundingpart: the luminance of the subtitles is excessively higher than that ofthe video as shown in a) or the luminance of the subtitles isexcessively lower than that of the video as shown in c). In order toprevent this problem, the luminance value of the subtitles may beadjusted using a transformation function similar or equal to that usedin video dynamic range mapping. Here, the receiver may use referenceinformation of the luminance of the subtitles. In other words, throughthe method proposed by the present invention, the broadcast transmittermay insert dynamic range information of a target subtitles reproductionenvironment or a subtitle production environment in XML metadata. Tothis end, since the dynamic range information of the target subtitlereproduction environment or the subtitle production environment areincluded in XML metadata (ebuttm:RefDynamicRange), the receiver mayperform comparison with the subtitle reproduction environment of thedisplay, convert the subtitle expression method to luminance suitablefor the environment of the receiver using suitable dynamic rangemapping, and reproduce the subtitles.

In addition, the luminance range of the video and the luminance range ofthe subtitles may be different and, in this case, the luminance range ofthe subtitles needs to be converted to suit the luminance range of thevideo. The receiver may use ebuttm:RefDynamicRange which is referenceinformation of the dynamic range as the reference information fordetermination and conversion.

If the color gamuts of the subtitle production environment and thereceiver do not match, the color of the subtitles may be changed.Through a method similar to the above-described method, conversion intoa color space suitable for the environment of the receiver may beperformed. If the color space of the subtitle production environment ora target color space considered to reproduce the subtitles and the colorspace of the display do not match, the receiver may convert the colorgamut of the subtitles to a displayable color gamut through the sameprocedure as color gamut mapping of the video. In addition, ifnecessary, the dynamic range mapping information or the color gamutmapping information may be delivered in the XML subtitles.

FIG. 5 is a diagram showing a method of transmitting metadata ofsubtitles according to an embodiment of the present invention. Morespecifically, an embodiment of XML subtitle metadata in EBU-TT-D isshown. The metadata of the subtitles may include information on at leastone of color gamut, dynamic range, EOTF and bitdepth.

In the embodiment, reference information of the subtitles may be setand, for example, the color gamut may be set to BT.2020, the dynamicrange may be set to 0.0001 ruts to 2000 nits, and the bitdepth may beset to 12 bits.

More specifically, the XML subtitle metadata may include color gamutinformation of the subtitles. The XML subtitle metadata may includeebuttm:RefGamut=“BT2020”, which may mean that the color gamut of thesubtitles is set to BT2020.

More specifically, the XML subtitle metadata may include dynamic rangeinformation of the subtitles. The XML subtitle metadata may includeebuttm:RefDynamicRange=2000 100 200000, which may mean that the dynamicrange of the subtitles is set to minimum luminance of 0.01 and maximumluminance of 2000 nits. Here, 200000 may mean a ratio of the minimumluminance to the maximum luminance. A detailed description thereof willbe given below.

More specifically, the XML subtitle metadata may include Electro-OpticalTransfer Function (EOTF) information of the subtitles, The XML subtitlemetadata may include ebuttm:EOTF=“SMPTE2084”, which may mean that theEOTF of the subtitles is set to SMPTE2084.

More specifically, the XML subtitle metadata may include bitdepthinformation of the subtitles. The XML subtitle metadata may includeebuttm:RefBitDepth=12, which may mean that the bitdepth of the subtitlesis set to 12 bits. In addition, the XML subtitle metadata may includeebutts:colorExtent=“0F040A” and ebutts:backgroundColorExtent=“010803” toadditionally set the extension field of the colors of the subtitles andthe background. That is, the metadata may be set to the colors of thesubtitles and the background to <tt:style xml:id=“BaseStyle”tts:color=“red”, ebutts:colorExtent=“0F040A”tts:backgroundColor=“yellow” ebutts:backgroundColorExtent=“010803” . . ./>. To this end, the color of the subtitles is red and the color of thebackground is yellow in the 8-bit based receiver, and the subtitleshaving the color of red =0×0FFF, green=0×0004 and blue=0×000A arerepresented in the 12-bit based receiver. In addition, the color of thebackground is yellow in the 8-bit based receiver and is red=0×oFF1,green=0×0FF8 and blue=0×003 in the 12-bit based receiver.

The metadata of the subtitles of the present invention is applicable toEBU-TT-D as described above and is also applicable to XML based subtitlestandards such as TTML, SMPTE-TT, CFF-TT, Youview and EBU-TT using asimilar method.

FIG. 6 is a diagram showing a detailed description of elements ofmetadata of subtitles according to an embodiment of the presentinvention. (a) shows a color gamut field. ebuttm:RefGamut included inthe metadata indicates the color gamut field considered upon producingthe subtitles and may be specified to an existing color gamut such asBT.709 or BT.2020 as show) in the figure. In addition, ebuttm:RefGamutmay provide information on an arbitrary color gamut by directlyspecifying CIExy coordinates. In the case of the arbitrary color gamut,CIExy coordinates (xRed, yRed, xGreen, yGreen, xBlue, yBlue, xWhite,yWhite) of red, green, blue and. white points may be delivered. Here, avalue corresponding to 10000 times an original coordinate value isdelivered according to value=originalValue *10000. If an existing colorgamut is used, BT709 or BT2020 attributes may be predefined and usedand, as shown in the figure, it is indicated that the color gamut isBT2020 using the <namedGamut> attribute. The color gamut field may beused as information for determining whether the color gamuts of thesubtitle production environment and the display environment (or video)match and, if necessary, information for color gamut mapping.

(b) shows a dynamic range field. The dynamic range field is an elementindicating the dynamic range of the video considered upon producing thesubtitles. The dynamic range field may include PeakBrightness,BlackLevel and ContrastRatio respectively indicating maximum luminance,minimum luminance and contrast ratio of the dynamic range. At this time,the ContrastRatio may indicate a ratio of maximum luminance to minimumluminance and may have a value of 10,000 in the case of 10,000:1, forexample. The PeakBrightness and the BlackLevel are expressed in nits(cd/m{circumflex over ( )}2), and BlackLevel may have a valuecorresponding to BlackLevel=OriginalValue *10000 in consideration ofBlackLevel of 1 or less.

If there is a standardized dynamic range such as HD, for example, anSMPTE reference HDTV standard may be utilized using <namedDynamicRange>attribute as shown in the figure. If a future HDR standard is released,a standardized dynamic range may be defined and used in anamedDynamicRange. The dynamic range field may be used as informationfor determining whether the dynamic ranges of the subtitle productionenvironment and the display environment (or video) match and, ifnecessary, information for dynamic range mapping.

The color gamut and the dynamic range may be used to provide informationon the subtitle production environment or to provide the color gamut anddynamic range information of target video/display.

(c) shows an EOTF field. The EOTF field may deliver EOTF informationused in association with the dynamic range. The EOTF field may deliverexisting EOTF information such as BT.1886 or SMPTE 2084. Although SMPTE2084 is used in the above-described embodiment, the EOTF element may beused to deliver an arbitrary EOTF. The EOTF field may be used forluminance linearization prior to dynamic range mapping.

FIG. 7 is a diagram showing a detailed description of elements ofmetadata of subtitles according to an embodiment of the presentinvention. (a) shows a bitdepth field. An UHD broadcast transmitter maytransmit a service based on a bitdepth of 8 bits or more in order toprovide improved image quality. For example, a 10-bit based service willbe provided in DVB UHD-1 phase 1 and a service based on at least 10 bitsmay be provided in MD-1 phase 2, to Which image quality elements such asWCG and HDR are added. Even in next-generation storage media such as BDUHD-FE or SCSA, a bitdepth of 10 bits or more may be similarlyconsidered. However, in the EBU-TTF-D standard, the expression method isrestricted to 8 bits. Accordingly, there is a need for a method ofdefining new bitdepth expression or a method of extending and expressinga bitdepth while maintaining an existing system. In the presentinvention, the method of extending and expressing the bitdepth whilemaintaining the existing system will be described.

As shown in (a), in the present invention, the metadata of the subtitlesmay represent a maximum bitdepth capable of being provided by thesubtitle system through ebuttm:RefBitDepth. The bitdepth may indicatethe number of bits of the information expressing the color. The range ofthe bitdepth may be from 8 to 16. For example, the bitdepth may be setto 8, 10, 12 or 16. If a rich color such as logo is not expressed,simple subtitles are used and, if a pallet having a subtitle color isrestricted to dithering, etc., a bitdepth of 8 or less may be used. Thatis, using this element, information on the pallet used in the subtitlesmay be delivered.

This field may be used as a criterion for comparing the bitdepth of thesubtitles and the bitdepth of the receiver or video in the preprocessingprocedure. In addition, this field may be used to inform the receiverthat a bitdepth of 8 bits or more is used or for the receiver to detectthat a bitdepth of 8 bits or more is used. If ebuttm:RefBitDepth is usedand has a value of 9 or more, the color may be expressed using tts:colorand ebuttds:colorExtent.

If it is necessary to support a high bitdepth for UHD with respect to anEBU-TT-D based subtitle service, that is, if ebuttm:RefBitDepth is setto a value of 9 or more in the present invention, an existing colorexpression method needs to be extended. In EBU-TT-D, the color isdefined using tts:color and, as shown in (b), the colors of red, green,and blue (and alpha) may be expressed using an 8-bit bitdepth throughthe color expression method defined in <ebuttdt:distributionColorType>.As a method of extending the existing 8-bit based color expressionmethod, as shown in (c), a method of further defining an extension fieldmay be used. That is, the higher 8 bits of the colors of red, green andblue (and alpha) representable by the bitdepth may be representedthrough tts:color and lower bits except for the higher 8 bits may berepresented through ebuttds:colorExtent. To this end, a receiverimplemented based on EBU-TT-D ver. 1, that is, a legacy receiver or a HDreceiver or fewer, which does not require a bitdepth of 8 bits or more,8-bit base color information may be interpreted through tts:color. Inaddition, in a UHD receiver, 8-bit base color information may beinterpreted through tts:color and a high depth exceeding 8 bits may beinterpreted through ebutts:colorExtent.

The extension field may be expressed using the existing expressionmethod without change, and, at this time, the lower bits except for thehigher 8 bits defined in ebuttm:RefBitDepth are expressed using 8 bits.An embodiment thereof was described above.

FIG. 8 is a diagram showing an additional description of elements ofmetadata of subtitles according to an embodiment of the presentinvention, In EBU-TT, SMPTE-TT and TTML, the color may be expressedusing rgb (r-value, g-value, b-value) along with #rrggbb. (a) shows anexample of metadata expression of the color of the subtitles in TTML andEBU-TT may define color expression using <ebuttdt:colorType> withrespect to the same method.

In this case, in order to represent the extended bitdepth, like theabove-described embodiment, a method of defining an extension field“tts:colorExtent” may be used. (b) and (c) are embodiments of definingtts:colorExtent in TTML. However, since the extension field does nothave an independent meaning, <namedColor> may not be used. As describedabove, in the case of EBU-TT, the extension field may be defined by<ebuttdt:colorTypeExtension>. For example, in a 12-bit based receiver,when the subtitles having the color of red=0×0FFF, green=0×0004,blue=0×000A are expressed, higher 8 bits of 12 bits may be representedusing the existing color expression method and the lower 4 bits may berepresented using the extension field. That is, the higher 8 bits may berepresented using tts:color and the lower 4 bits may be representedusing tts:colorExtent.

In the metadata of the subtitles according to the embodiment of thepresent invention, the extension field may be added to extend the colorgamut and express subtitles having various colors, while maintaining theexisting color expression method.

FIG. 9 is a block diagram showing a broadcast transmitter according toan embodiment of the present invention. The broadcast transmitter 1701according to the present invention may include an encoder 1702, amultiplexer 1703 and/or a transmission unit 1704.

The resolution of video data input to the broadcast receiver 1701 may beUHD, HD or SD. In addition, subtitle information input to the broadcastreceiver 1701 may be described in XML. The video data input to thebroadcast receiver 1701 may be encoded by the encoder 1702. Atransmitter may use high efficiency video coding (HEVC) as an encodingmethod of the video data. The transmitter may synchronize and multiplexthe encoded video data and XML subtitles using the multiplexer 1703.Here, the XML subtitles may include metadata of the subtitles asdescribed above and may include information on the color gamut, dynamicrange, EOTF and bitdepth of the subtitles.

The transmission unit 1704 may transmit a transport stream output fromthe multiplexer 1703 as a broadcast signal. Here, the transport streammay be subjected to channel coding and modulation and then transmittedas the broadcast signal.

FIG. 10 is a block diagram showing a broadcast receiver according to anembodiment of the present invention. The broadcast receiver 1801according to the present invention may include a reception unit 1802, ademultiplexer 1803 and/or a decoder 1804.

A broadcast signal received by the reception unit 1802 may bedemodulated and then subjected to channel decoding. The channel-decodedbroadcast signal may be input to the demultiplexer 1803 to bedemultiplexed into a video stream and a subtitle stream. The output ofthe demultiplexer may be input to the decoder 1804. The decoder mayinclude a video decoder and an XML parser. That is, the video stream maybe decoded by a video decoder and the subtitle stream may be decoded bya subtitle decoder or parsed by an XML parser, thereby outputting videodata and subtitle data. Here, the video decoder and the XML parser mayexchange metadata with each other. That is, the XML parser may comparethe metadata of video and the metadata of the subtitles as describedabove. Here, the metadata to be compared may include dynamic ranges,color gamuts, bit depths, etc. of the video and the subtitles. Inaddition, the metadata of the display of the receiver and the metadata.of the subtitles may be compared. Here, the metadata. to be compared mayinclude dynamic ranges, color gamuts, bit depths, etc. of the displayenvironment and the subtitles.

In particular, in the present invention, if a wide color gamut (WCG) anda high dynamic range (HDR) of the UHD image quality elements areincluded in the service (e.g., DVB UHD-1 phase 2, BD UHD-FE, etc.), itis possible to provide information on the image quality elements to thereceiver as subtitle production criteria. If the subtitle productionenvironment and the display environment are different, the receiver mayappropriately modify the color or luminance of the subtitles accordingto the display environment. The broadcast receiver may modify theexpression method of the XML subtitles in corresponding to theabove-described video elements. The video data and the subtitle data aresynchronized and displayed by the receiver.

FIG. 11 is a diagram showing the configuration of a broadcast receiveraccording to an embodiment of the present invention in detail. Thebroadcast receiver may include a reception unit 1901, a demodulator1902, a demultiplexer 1903, a video decoder 1904, an XML subtitledecoder 1905, an audio/video/subtitle (A/V/S) synchronizer 1906, asystem information (SI) processor 1907, a graphics engine 1908 and/or adisplay processor 1909.

The reception unit 1901 may receive a broadcast signal transmitted bythe transmitter. The received broadcast signal may be input to thedemodulator 1902.

The demodulator 1902 may demodulate the broadcast signal and output atransport stream (TS). The TS may be input to the demultiplexer 1903 tobe demultiplexed. The demultiplexed TS may include an HEVC bitstream,XML subtitles and system information (SI). Here, the XML subtitles mayinclude metadata.

The video decoder 1904 may receive and decode the HEVC bitstream andoutput a video frame.

The XML subtitle decoder 1905 may receive the XML subtitles and extractsubtitles. The XML subtitle decoder 1905 may parse the metadata includedin the XML subtitles and compare the parsed metadata with the metadataof the video or the display environment. Here, the metadata to becompared may include a dynamic range, a color gamut, a bit depth, etc.The XML subtitle decoder 1905 may convert the metadata of the subtitledepending on whether the compared metadata matches. The XML subtitledecoder 1905 may deliver, to the graphics engine, the metadata of thesubtitles and the subtitles without separate transformation if thecompared subtitle data matches. In contrast, if the compared subtitledata does not match, the XML subtitle decoder 1905 may convert themetadata of the subtitlse and deliver the subtitle data and theconverted metadata to the graphics engine. To this end, matching betweenthe subtitles and the video can be enhanced.

The system information processor 1907 may receive SI information outputfrom the demultiplexer 1907 and extract on screen display (OSD)information,

The graphics engine 1908 may receive the subtitles and the metadata ofthe subtitles from the XML subtitle decoder 1905 and output a subtitleimage. The subtitle image is generated based on the subtitles and themetadata of the subtitles and the color, luminance, etc. of the outputsubtitle image may be changed depending on whether the metadata of thesubtitles is converted.

The display processor 1909 may receive the video frame and the subtitlesand output a display frame. The display processor 1909 may receive theOSD information in addition to the video frame and the subtitles andoutput the display frame. The output display frame may be displayed byan image output device and may be displayed along with the XML subtitlesand video frame described in the present invention.

FIG. 12 is a diagram showing a method of transmitting a broadcast signalincluding XML subtitles according to an embodiment of the presentinvention. The method may include step S2210 of encoding a video streamand generating video data, step S2220 of generating a broadcast signalincluding the generated video data and subtitle information and stepS2230 of transmitting the generated broadcast signal.

Step S2210 of encoding the video stream and generating the video datamay include receiving the video stream having resolution of UHD, HD orSD, encoding the video stream and generating the video data. Here, thevideo stream may be encoded by high efficiency video coding (HEVC). SMLsubtitle data may also be generated. As described above, the XMLsubtitle data may include metadata of the subtitles and the metadata mayinclude XML subtitle related data suitable for a UHD broadcast. That is,the metadata may include information on dynamic range, color gamut, bitdepth and EOTF information, which may have values corresponding to awide color gamut (WCG) and a high dynamic range (HDR) of the UHDbroadcast.

Step S2220 of generating the broadcast signal including the generatedvideo data and the subtitle data may include building a broadcast signalframe and generating a broadcast signal using a modulation process.

Step S2230 of transmitting the generated broadcast signal may includetransmitting a transport stream as a broadcast signal.

FIG. 13 is a diagram showing a method of receiving a broadcast signalincluding XML subtitles according to an embodiment of the presentinvention. The method of receiving the broadcast signal including theXML subtitles may include step S2310 of receiving a broadcast signal,step S2320 of demultiplexing the received broadcast signal into videodata and subtitle data and step S23330 of decoding the video data.

Step S2310 of receiving the broadcast signal may include demodulatingthe broadcast signal received through the reception unit and performingchannel decoding with respect to the broadcast signal.

Step S2320 of demultiplexing the received broadcast signal into thevideo data and the subtitle data may include demultiplexing thechannel-decoded broadcast signal into the video data and subtitle datausing the demultiplexer.

Step S2330 of decoding the video data and the subtitle data may includedecoding the video data using a video decoder and acquiring the videodata. In this step, the subtitle data may be acquired using a subtitledecoder or an XML parser. The receiver may receive XML subtitles andextract subtitles. The receiver may parse and compare the metadata.included in the XML subtitles with the metadata. of the video or displayenvironment. Here, the metadata to be compared may include a dynamicrange, a color gamut, a bit depth, etc. The receiver may convert themetadata of the subtitles depending on whether the compared metadatamatches. The receiver may deliver, to the graphics engine, the metadataof the subtitles and the subtitles without separate conversion if thecompared subtitle data matches. In contrast, if the compared subtitledata does not match, the receiver may convert the metadata of thesubtitles and deliver the subtitle data and the converted metadata tothe graphics engine. To this end, it is possible to enhance matchingbetween the subtitles and the video.

Since UHD considers various properties as the image quality elements,the diversity of content and receiver are highly likely to be increased.However, in the case of text based subtitles, it is not efficient that aunique version be made for each of various video or receiver types. TheXML subtitles are applicable independently of the size of video but doesnot consider change in WCG and HDR. However, using the method of thepresent invention, it is possible to provide a service having the samequality using a single XML subtitle service with respect to variouscolor gamuts and dynamic range environments. Although the presentinvention is described from the viewpoint of a receiver, the presentinvention may be used even in production or subtitle productionenvironments. In addition, the present invention may be used in allbroadcast services (e.g. DVB UHD-1 service) using XML based subtitleservice in addition to an IP streaming based service.

Although the description of the present invention is explained withreference to each of the accompanying drawings for clarity, it ispossible to design new embodiment(s) by merging the embodiments shown inthe accompanying drawings with each other. And, if a recording mediumreadable by a computer, in which programs for executing the embodimentsmentioned in the foregoing description are recorded, is designed innecessity of those skilled in the art, it may belong to the scope of theappended claims and their equivalents.

An apparatus and method according to the present invention may benon-limited by the configurations and methods of the embodimentsmentioned in the foregoing description. And, the embodiments mentionedin the foregoing description can be configured in a manner of beingselectively combined with one another entirely or in part to enablevarious modifications.

The image processing method according to the present invention may beimplemented as code that can be written to a processor-readablerecording medium and can thus be read by a processor. Theprocessor-readable recording medium may be any type of recording devicein which data can be stored in a processor-readable manner. Examples ofthe processor-readable recording medium include a ROM, a RAM, a CD-ROM,a magnetic tape, a floppy disk, an optical data storage, and a carrierwave (e.g., data transmission over the Internet). The computer-readablerecording medium can be distributed over a plurality of computer systemsconnected to a network so that processor-readable code is writtenthereto and executed therefrom in a decentralized manner. Functionalprograms, code, and code segments needed to realize the embodimentsherein can be construed by one of ordinary skill in the art.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims. Such modifications should notbe individually understood from the technical spirit or prospect of thepresent invention.

Both apparatus and method inventions are mentioned in this specificationand descriptions of both of the apparatus and method inventions may becomplementarily applicable to each other.

[Mode for Invention]

Various embodiments have been described in the best mode for carryingout the invention.

INDUSTRIAL APPLICABILITY

The present invention is repetively available in broadcast and videosignal processing fields.

The invention claimed is:
 1. A method of transmitting a broadcast signalby a broadcast transmitter, the method comprising: generating video datathat correspond to at least one of SD resolution, HD resolution, and UHDresolution; encoding the generated video data; generating subtitle datathat is associated with a single resolution of the video data, whereinthe subtitle data includes color information, dynamic range informationof subtitle text and bit depth information so that a receiver is able tomodify at least one color or a brightness of the subtitle text when aresolution of the video data, that is displayed with the subtitle text,is different from the single resolution of the video data, wherein thecolor information represents color gamut information for the subtitletext, and the bit depth information, that represents one or more colorsfor the subtitle text, has value of which range is defined from 1 to 16,for a value of the bit depth information, that is greater than 8, thesubtitle data further includes extended color information; multiplexingthe encoded video data and the generated subtitle data; and transmittingthe generated broadcast signal including the multiplexed video data andsubtitle data.
 2. The method according to claim 1, wherein the subtitledata is XML subtitle data.
 3. The method according to claim 2, whereinthe XML subtitle data includes the subtitle text and subtitle metadata.4. The method according to claim 3, wherein the subtitle metadataincludes information corresponding to a wide color gamut and a highdynamic range for a high-quality broadcast.
 5. A method of receiving abroadcast signal by a broadcast receiver, the method comprising:receiving the broadcast signal including video data and subtitle data,the video data corresponding to at least one of SD resolution, HDresolution, and UHD resolution; demultiplexing the broadcast signal intothe video data and the subtitle data, the subtitle being associated witha single resolution of the video data, wherein the subtitle dataincludes color information, dynamic range information of subtitle textand bit depth information, wherein the color information representscolor gamut information for the subtitle text, and the bit depthinformation, that represents one or more colors for the subtitle text,has value of which range is defined from 1 to 16, for a value of the bitdepth information, that is greater than 8, the subtitle data furtherincludes extended color information; decoding the video data; when aresolution of the video data, that is displayed with the subtitle text,is different from the single resolution of the video data, modifying atleast one color or a brightness of subtitle text in the subtitle data byusing the color information and dynamic range information of thesubtitle text; and displaying the decoded video data with the subtitletext having at least one modified color or a modified brightness.
 6. Themethod according to claim 5, wherein the subtitle data is XML subtitledata.
 7. The method according to claim 6, wherein the XML subtitle dataincludes the subtitle text and subtitle metadata.
 8. The methodaccording to claim 7, wherein the subtitle metadata includes informationcorresponding to a wide color gamut and a high dynamic range for ahigh-quality broadcast.
 9. The method according to claim 7, wherein thevideo data further includes video metadata.
 10. The method according toclaim 8, further comprising detecting whether the subtitle metadata andthe video metadata match.
 11. The method according to claim 10, furthercomprising converting the subtitle metadata if the subtitle metadata andthe video metadata do not match.
 12. A device for transmitting abroadcast signal, the device comprising: an encoder for encoding videodata that correspond to at least one of SD resolution, HD resolution,and UHD resolution; a multiplexer for multiplexing the encoded videodata and subtitle data, the subtitle data being associated with a singleresolution of the video data, wherein the subtitle data includes colorinformation, and dynamic range information and bit depth information ofsubtitle text so that a receiver is able to modify at least one color ora brightness of the subtitle text when a resolution of the video data,that is displayed with the subtitle text, is different from the singleresolution of the video data, wherein the color information representscolor gamut information for the subtitle text, and the bit depthinformation, that represents one or more colors for the subtitle text,has value of which range is defined from 1 to 16, for a value of the bitdepth information, that is greater than 8, the subtitle data furtherincludes extended color information; and a channel coding and modulationmodule for transmitting the broadcast signal including the multiplexedvideo data and subtitle data.
 13. A device for receiving a broadcastsignal, the device comprising: a demodulator for demodulating thebroadcast signal including video data and subtitle data, the video datacorresponding to at least one of SD resolution, HD resolution, and UHDresolution; a demultiplexer for demultiplexing the broadcast signal intothe video data, and the subtitle data, the subtitle being associatedwith a single resolution of the video data, wherein the subtitle dataincludes color information, and dynamic range information of subtitletext; a first decoder for decoding the video data; a second decoder formodifying at least one color or a brightness of subtitle text in thesubtitle data by using the color information, and dynamic rangeinformation and bit depth information of the subtitle text when aresolution of the video data, that is displayed with the subtitle text,is different from the single resolution of the video data, wherein thecolor information represents color gamut information for the subtitletext, and the bit depth information, that represents one or more colorsfor the subtitle text, has value of which range is defined from 1 to 16,for a value of the bit depth information, that is greater than 8, thesubtitle data further includes extended color in information; and adisplay processor for displaying the decoded video data with thesubtitle text having at least one modified color or a modifiedbrightness.